Cloud computing treats the resources on the Internet as a unified entity, cloud. A cloud storage system is considered as a large scale distributed storage system that consists of many independent storage servers. Storing data in a third party's cloud system causes serious concern on data confidentiality. In order to provide strong confidentiality for messages in storage servers, a user can encrypt messages by a cryptographic method. General encryption schemes protect data confidentiality but also limit the functionality of the storage system because a few operations are supported over encrypted data. In this paper, the authors address the problem of forwarding data to another user by storage servers directly under the command of data owner.